For example, in the process of manufacturing a Cu(In,Ga)(S,Se)2 semiconductor layer of a CIS solar module, the method of thermal vapour deposition (hereinafter referred to as “TVD”) is well established to deposit Selenium (Se) thin films on large surface substrates.
In industrial production processes for manufacturing devices comprising a thin film of thermal vapour deposited material several general requirements have to be observed. For example, in order to be effective, an industrial manufacturing process requires a sufficiently high deposition rate which can be achieved when the TVD is performed at high temperatures. A further requirement relates to durability of the apparatus employed for TVD. The former requirement contradicts the latter since higher temperatures lead to higher wear and a reduced life cycle of the apparatus. In addition, higher temperatures increase the risk of contaminations of the material to be deposited by means of TVD, especially when aggressive materials such as Selenium (Se) are to be deposited. Particularly, in the field of solar cell semiconductor CIS thin films such contaminations may cause impurity traps in the semiconductor deteriorating the performance. Finally, high corrosion attack due to high processing temperatures makes it difficult to achieve constancy in apparatus performance which is a further requirement of industrial manufacturing processes.
DE 100 21 530 C1 describes a vapour source with an elongated vapour outlet pipe and a heating rod provided coaxially in the interior of the vapour outlet pipe. The vapour source of DE 100 21 530 C1 is specifically designed for the manufacturing process of CIS thin film solar cells. The material to be deposited is heated in two crucibles whereby a vapour is generated and the vapour is supplied to the heated vapour outlet pipe comprising outlet openings through which the vapour escapes from the vapour source for being deposited on a substrate. It is mentioned in DE 100 21 530 C1 that several vapour sources can be used in a serial arrangement to deposit different materials in the manufacturing process of a CIS solar cell.
EP 1 424 404 A describes a thermal evaporation apparatus comprising an electrically heated melting crucible in which the material to be deposited is stored and melted to generate the vapour. The vapour is received in a vapour pipe comprising outlet openings allowing the vapour to escape from the vapour pipe. The vapour pipe is surrounded by a heater, and radiation reflectors are arranged in order to direct the heat provided by the heater to the vapour pipe.
There is a need for a thermal evaporation apparatus which is capable of depositing any material, including aggressive materials, such as Selenium (Se), at high deposition rates.
There is also a need for a thermal evaporation apparatus which can be operated at high temperatures up to and above 400° C., and even much higher, in order to achieve high deposition rates.
There is further a need for a thermal evaporation apparatus which is resistant to wear even at high temperatures and in the presence of aggressive materials such as Selenium (Se).
There is a still further need for a thermal evaporation apparatus which is specifically suited for being employed in the manufacturing process of CIS solar cells.